Re: what is a fossil

["King, Norm" <nking.ucs@smtp.usi.edu>]

I disagree with Bonnie's characterization of what a fossil is.  Much of 
the discussion and confusion that followed her posting resulted, I think, 
from the unsatisfactory nature of those characterizations.  She said 
(6/18/97; 3:27p):

>there are currently two working definition as to what constitutes a 
>fossil:
>1.  remains from an animal or plant that have been remineralized.
>2.  any dead animal or plant

Of course, people with different backgrounds will come up with different 
answers about what is a fossil.  Only on rare occasions have I heard it 
claimed that any modern object qualifies as a fossil, regardless of its 
state of preservation.  We might as well say that a shovel or half-eaten 
sandwich that fell into an asphalt seep 5 years ago and became permeated 
with preservative hydrocarbons is a fossil.

Conversely, I have always discussed the "unaltered" state of preservation 
for fossils in my paleo course.  It is common for very old materials to 
consist of the original shell, bone, etc. material--the invertebrate 
fauna of Late Cretaceous age at Coon Creek, TN for example, and maybe 
some dinosaur bone that is so little altered that some people have 
thought (although it is apparently not the case) there might be 
recognizable original DNA in them.  I don't think it is right to say that 
any remains of dinosaurs are not fossils.

Bonnie continued:

>obviously, these are two ends of a very long very complex spectrum of
>processes that turn fossils type 2 into type 1 (you might think of
>them as sensu stricto and sensu lato).  I have personally found
>remains that fully qualify as #1 that are less than 5 YEARS OLD!!
>SOME AS YOUNG AS 3 MONTHS!!! so age plays little role.  the speed
>at which fossilization (sensu stricto i.e. remineralization occurs)
>can be very rapid in some environments, such as saline lakes.
>if you examine the fossil record, preservation is enhanced in areas
>where the fossilization is very rapid. 

>conversely, there are 200,000 year old fossils in which the 
>bone mineral and its organic component are 98% pristine.  
>so again age is not a guideline.  

My opinion is that alteration need not occur, and that age is not only a 
factor, it is THE critical factor.  Moreover, Cretaceous carbonized 
leaves are surely fossils, but I don't think they are really 
remineralized.  Also, I think that all workers consider insects in amber 
to be fossils, in spite the lack of remineralization.

Lenore Adler provided this definition (6/24/97; 2:54p):

>The definition I use is "any evidence of life, more than 10,000 years 
>old" 
>that takes into consideration the many modes of fossilization, and 
>remains that are not part of the animal or plant (footprints, 
>impressions, burrows, shells, gastroliths, etc.)...Lenore

This definition is concise, and obviates the unending objections, 
exceptions, qualifications, and questions that arise from Bonnie's 
definition.  I would add simply that a fossil can be any DIRECT evidence 
of past life, so as to exclude derivatives of organic processes and 
alteration such as coal and hydrocarbons.

Finally, suffice it to say, after this discussion, that there are well 
over two current working definitions as to what a fossil is, some better 
than others.  Paleontologists who study remains that aren't very old 
might require only the "alteration" criterion, but I think it breaks down 
too quickly (witness what has happened just in this group of discussants) 
to adopt it.  Then, I don't know what to say about this proposition, 
which follows from the lack of a minimum age criterion:  "This is a 
dinosaur bone, but it is not a fossil."  That would be an absurd 
proposition, in my opinion.


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Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu